Field of the Invention
The present invention relates to a device for establishing a current in an analogue part of an integrated logic and analogue circuit. More particularly, the present invention relates to such a device designed for establishing such a current in a so-called "intelligent" integrated power circuit.
Integrated circuits are known comprising input and/or output pins designed to receive or transmit digital signals which are processed or formulated in a logic part of the circuit, and to control analogue output quantities. The so-called "smart" power circuits are examples of such circuits in which digital control and/or diagnostic signals are processed in a logic part adjoining an analogue part comprising a power transistor controlling the flow of a powering current in a load outside the circuit.
In such a circuit there may be a need for a reference current, for example in order to ensure a correct biasing of a sub-circuit, or in order to limit, direct or regulate an output current powering a load. Now, present methods of manufacturing integrated circuits do not allow the direct construction of precise internal current sources. Recourse must then be had to internal methods of adjustment or to means of adjustment based on external components such as a resistor.
Internal methods of adjustment, which call upon the use of so-called "ZAP" Zener diodes, fuses or programmable memories, bring about an increase in the surface area of the chip embodying the integrated circuit. Furthermore, the implementing of the method of adjustment increases the manufacturing time and number of rejects when sorting the manufactured chips. This solution is not viable when seeking as economical a manufacture as possible.
Power supplies use frequently external components like external resistors or application of external voltage to adjust some parameters. As an example, patent application EP 103 455 describes a power supply unit in which regulated output voltage can be switched between two operating values (high and low voltage) by application of a control voltage to a control terminal. In the same way, document "Les alimentations de laboratoire" published in "Electronique Applications" n.degree.24 (June 1982) teaches a power supply in which remote control of current is adjusted by a voltage or a resistor connected between specialised pins of the circuit.
However, use of an external resistor entails the presence of an additional specialised pin on the casing of the chip and of the corresponding connection lug on the chip itself, arrangements which also raise the price of the manufactured product. The two known methods are not therefore economical, this being especially harmful in the case of low cost price, high volume manufacture such as encountered in automobile electronics.
The aim of the present invention is therefore to construct a device for establishing a current in an analogue part of an integrated logic and analogue circuit, which calls upon neither an internal adjustment nor an external resistor connected up to a specialised pin of the circuit.
The aim of the present invention is also to construct such a device which is of especially economical construction.